In recent years, as use of portable electronic devices (e.g., mobile phones and digital cameras) becomes ubiquitous, much effort has been put into reducing dimensions of portable electronic devices. Moreover, as dimensions of charged coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) based optical sensors are reduced, dimensions of imaging lenses for use with the optical sensors must be correspondingly reduced without significantly compromising optical performance. Image quality and size are two of the most important characteristics for an imaging lens.
Taiwanese patent No. I254140 discloses a conventional imaging lens that includes four lens elements and having a F-number of 4.0. However, the amount of light entering such imaging lens is insufficient to obtain a satisfactory imaging quality and the system length of such imaging lens is up to 12 mm, which disfavors reducing the thickness of portable electronic devices such as mobile phones with a slim profile.
Therefore, technical difficulties of a miniaturized imaging lens are higher than those of traditional imaging lenses. Producing an imaging lens that meets requirements of consumer electronic products with satisfactory optical performance is always a goal in the industry.